The present invention relates to a permanent-magnet brushless DC motor, and more particularly to a brushless DC motor having opposed pairs of axial magnetic field type permanent-magnets which achieves low and medium revolving speed, high torsional force and high power.
Regular electric motors are commonly of "radial magnetic field" type. Because the rotor of this design of electric motors receives pushing force from one side only, the number of poles and space utilization percent of these conventional electric motors are low. There is known another type of electric motor using an "axial magnetic field". However, these electric motors are AC single phase, two-phase or three-phase synchronizing/synchronizing induction motors, permanent-magnet step motors, magnetic resistance motors rather than DC motors or permanent-magnet synchronizing motors.
Due to improvement in steel material magnetization, and availability and cost reduction of rubidium borax rare earth magnetic metal, permanent-magnet DC motors have been intensively used in different fields. Because high intensity magnetic materials are intensively used, permanent-magnet DC motors are relatively smaller, thinner and lighter than equivalent AC motors, and save more energy than equivalent AC motors. In certain application fields, the performance curve of permanent-magnet DC motors is superior to that of AC motors. Furthermore, fast development of the semi-conductor industry in recent years has greatly improved the application of permanent-magnet brushless DC motors in electronic, digital servo control fields. However, no brushless DC motors having opposed pairs of axial magnetic field type permanent-magnets have previously been proposed.